Place the vegetable oil in a large clay pot.
Drain the soaked rice and add to the clay pot. Toss with the oil until coated and spread into an even layer.
Add the chicken stock, cover, and bring to a simmer over medium heat (if using a clay pot- begin on low and slowly adjust to medium).
Once simmering, reduce heat to medium low and allow to cook undisturbed just until the liquid reaches the level of the rice, about 10-15 minutes.
Arrange the marinated chicken across one section of the rice in a single layer to allow for even cooking.
Arrange the sliced mushrooms across another section of the rice.
Arrange the sliced sausage across another section of the rice.
Place the lid back on the pot, reduce heat to low, and continue to cook until the chicken is cooked through, about 15 minutes, and the rice is tender.
Arrange the quartered or halved bok choy over the ingredients, place the lid back on the pot, and cook for another 3 minutes to steam.
In a small bowl, whisk together the oyster sauce, soy sauce, dark soy sauce, sesame oil, and sugar until combined.
Remove the lid, drizzle the oyster sauce mixture evenly over the rice and ingredients, slightly increase the heat, and continue to cook uncovered for another 1-2 minutes until the rice is toasted along the bottom.
Remove from heat and lightly toss together the ingredients to combine, scraping along the bottom while still warm to remove any crispy bits of the rice.
Serve immediately with a sprinkling of thinly sliced green onions.